Geology

• Mineralogy


  A scientific study of minerals, structure (chemical and crystalline), properties (physical), processes (origin, formation & occurrence), classification and distribution, and uses

  
• Minerals


  Naturally occurring, inorganic, solid element or compound crystalline substance, has definite atomic structure and chemical composition

  
• Over 400 minerals exist in earth crust
• All minerals are composed of oxygen, silicon, aluminum, iron, calcium, potassium, sodium and magnesium
• Classifications and Mineral Groups


  • Rock Forming Minerals
  • Ore Forming Minerals

  
• Rock Forming Minerals


  • Minerals found in abundance of earth crust
  • Forms igneous, sedimentary, or metamorphic rocks

  
• Ore Forming Minerals


  • Minerals that are or economic values
  • Limited mode of occurrence
  • Formed by more unusual processes
• Physical Properties of Minerals


  • Not constant in most of the minerals
  • Due to the stain or impurities in the minerals
  • May indicate that mineral has undergone peculiar phenomena

  
• Color


  Development of series or prismatic colors by turning about in light
• change of Colors

  Similar to play of colors but slower rotation
• Change of Colors


  Show rainbow colors either in the interior or on the surface
• Azurite


  • Bright blue color
• Streak


  • Color of mineral powder
  • Nearly constant than the color
  • Determined by marking unglazed porcelain or simply by scratching with a knife and observing the powder color
• Hematite


  • Produces a red streak
• Lustre


  • Description of how much a mineral reflects light
  • Metallic (Shiny): Classy (vitreous), Metallic, Pearly
  • Non-metallic (Dull)

  
• Structure and Form (Habit)


  Denote the shape and form of minerals

  
• Hardness


  • Resistance of minerals to abrasion or scratching
  • Measured relative to a scale of ten of minerals (Mohs Hardness Scale)
• Gypsum

  • Mohs Hardness 2, can be scratched by a fingernail
• Quartz


  • Mohs Hardness 7.0, can scratch window glass but can be scratched by Topaz
• Specific Gravity


  • The density of the mineral compared to the density of water
  • Metallic minerals have high SG, non-metallic minerals have lower SG
• Cleavage


  • Tendency of a crystallized mineral to break along certain definite planes yielding more or less smooth surfaces
  • Cubic: 3 cleavages
  • Octahedral: 4 cleavages
  • Dodecahedral: 6 cleavages
  • Basal: 1 cleavage

  
• Fracture


  • Defined as the appearance of its broken surface
  • Conchoidal: concentric rings or curved surface
  • Even: smooth and flat
  • Uneven: irregular surface
  • Splintery: breaks with a rough
• Tenacity


  Behavior of mineral when deformed or broken
• Crystallography


  • The science concerned with the formation, properties, and structure of crystals
  • Deals with the geometric forms of crystals

  
• Mineral Crystal System


  • Also called Mineral Habits
  • Refers to the way crystals form within a specific mineral

  
• Diamond


  • Two pyramids attached at their bases
• Quartz


  • Has six sides
• Crystallized


  Mineral occurs in the form of well-defined crystals

  
• Amorphous


  Shows absolutely no signs or evidence of crystallization
• Crystalline


  Well-defined crystals are absent but a tendency towards crystallization is present
• Symmetry


  • Describes the repetition of structural features
  • Two general types: Translational and Point
• Translational Symmetry


  Periodic repetition of structural feature across a length or through an area or volume
• Point Symmetry


  • Periodic repetition of structural at a point
  • Reflection, rotation, and inversion are examples
• Lattices


  • Directly related to translational symmetry
  • A network or array composed of single motif that has been translated and repeated at fixed intervals throughout space
• Bravais Lattices


  • There are only fourteen (14) different lattices that may be formed in a 3D space
  • Divided into six (6) crystal systems
  • Has three (3) types: Primitive, Face-centered, Body-centered
• Crystal Systems


  • All minerals form crystals in one of the systems and are defined by a combination of three factors: Number of axis, Length of axis, Angles the axes meet
  • Axis A is usually the shortest, while C is the longest axis

  
• Types of Crystal Forms

  • Monohedron
  • Parallelohedron
  • Didedron
  • Disphenoid
  • Prism
  • Pyramid
  • Dipyramid
  • Trapezohedron
  • Scalenohedron
  • Rhombhohedron
  • Tetrahedron
• Mineral Families

  • Quartz Family
  • Feldspar Family
  • Pyroxene Group
  • Hornblende
  • Mica Group
  • Calcite
  • Garnet Family